EEVEE subsurface scattering (SSS) causes artifacts/banding
I discovered through more experimentation that subsurface value set to 1.0 is extremely high.  Values below 0.3 don't exhibit these artifacts.  Also:


moving the light further away from the object reduces artifacts even at sss=1
it's not necessary to turn on screen space reflection/refraction 
SSS translucency does work.  I don't know why it wasn't working when I created those screenshots.  Maybe I just needed to reboot, or maybe I had some weird settings.